Tom Székely, P.E., LEED AP

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December 1, 2005

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The Shareholder/Unit Owner Board Member Survival Manual, or, Engineering for Dummies – Part 2


So, boys and girls, when I closed last month, I described how the low-flush toilets  which came upon the scene in response to the 1974 Clean Water Act started to cause problems in heretofore  trouble-free plumbing systems serving penthouses in high-rise residential buildings.  Also, as I hinted at in the introduction to the explanation of that problem, the solutions, if not carefully effected, could cause problems of their own, which brings us to today’s lesson.


If there’s a problem of inadequate water pressure, something has to be done to increase it, but what?  Well the obvious solution is to install a pump to increase system pressure, and I have in fact done such, providing a pump in a parallel bypass line right where the water main enters a dwelling, but this presupposes a single main to a dwelling unit, which is not usually the case. 


In fact, in high-rise multifamily dwellings there are usually several plumbing risers serving any given dwelling unit, and any solution only becomes workable when the unit is re-piped to be served from (pipe size permitting) only one riser or the several risers are manifolded together at the inlet to a “single” pressure booster pump. “Single” is in quotes because whatever’s done to the cold water also needs to be done to the hot water, and therein lies one of the gotchas mentioned in the last issue.  This trap is actually a secondary effect of trying to do the right thing, that right thing being a way to solve the problem without the noise and electrical consumption of a constant-running pressure booster pump.


One solution is to provide a flow switch in the dwelling’s water service piping to operate the booster pump whenever any tap is opened, which is in fact what I’d done when I provided a booster pump in a parallel bypass line.  A better way  is to provide a pressure tank/pump package where the pump pressurizes a tank which is used to provide the system’s pressure boost, and is recharged by the pump when the pressure falls below a predetermined setting.  If all the system’s components are correctly selected and adjusted, there can be a savings in energy consumption as the pump does not necessarily run continuously so long as there is flow in the system.  This also saves wear and tear on the pump, and makes for a little less mechanical noise than a pump which runs as long as water is flowing in the system.


This has the secondary benefit of allowing (gas pipe size or electric service capacity permitting) a single pressure booster package, with that package also feeding the inlet of a domestic hot water heater for in-dwelling generation of hot water. (At which point the whole thing starts to look a lot like a single family home served by a well but there are now tertiary gotchas about check valves and expansion tanks at the inlet of the domestic hot water heater, which are beyond the scope of this particular discussion.)


Yet another way is to provide another such package for the dwelling’s hot water service main or manifold, which brings us back to the secondary gotcha mentioned a while back.


Engineering, since it’s an applied science, defers rather more to experience than does, say, Quantum Mechanics, and  a great deal of that has to do with how materials and systems behave under varying environmental conditions.  One of the things which contributed to the less than satisfactory conclusion of Titanic’s maiden voyage was how the brittleness of the hull’s steel was exacerbated by the frigid water of the North Atlantic.  This event was the first in a series of such events, which were to become experience as the keel of one Liberty Ship after another broke in the same waters during convoy runs to Murmansk in World War Two.


The point here is that the behavior of certain steel in moderately cold temperatures is a warning flag to be applied to other materials in any situation other than room temperature.  After all, we already know enough to design and install piping systems to allow for expansion as temperature increases . . . don’t we?


To put it more directly, and to relate it  to the particular problem I saw in the field which was the predicate for this piece, plastic, while it’s a great material at room temperature, has a tendency to soften at even moderately elevated temperatures, to the extent that while making a spatula out of plastic for use with Teflon-lined pans might be marginally workable, making the pan itself from plastic is not a very good idea.  I mean, even boiling water in a microwave oven in the wrong kind of plastic cup has been known to convert what was a cup into a lump of shapeless polymer.


What do you suppose would make someone think it was a good idea to connect a pressure booster package to an existing copper hot water system via the use of plastic piping and fittings?


While such things fall into the category of the “they weren’t” answer to the “what were they thinking?” question, I have been affected by the results of just such a situation after a pressure booster package manufacturer was involved in a lawsuit where a plumber connected one of the manufacturer’s systems in just such a manner, and, guess what?  The connections failed, spilling water down through the apartments below.


Of course, not having had anything to do with this debacle, it shouldn’t have affected me, except for the fact that the pressure booster package manufacturer, whose printed specifications showed the equipment rated for use at temperatures up to 200 degrees Fahrenheit, suddenly decided the systems would be out of warranty if installed in domestic hot water systems.


Understand that these are systems where the utilization temperature must be below 120 degrees Fahrenheit to prevent burns, and where storage temperatures are routinely just a little above 140 degrees Fahrenheit in order to kill Legionnaire’s disease bacteria.  Even domestic hot water from instantaneous coils in space heating boilers never leaves the boiler room at temperatures much above 140 degrees Fahrenheit because of thermostatic mixing valves at the discharge of the coil.


This becomes all the more perplexing here in New York City where getting plastic piping into even a domestic cold water system or even a sanitary and waste piping system takes something of an effort to do legally.


Do utterances we have all heard, such as “Performed by qualified professional driver on closed course.” or, “Don’t try this at home.” seem to be able to be related to the issues brought up in this narrative?


Is it not the point of such admonitions that bad things usually happen when they are ignored? 


Hooking a pressurizer package into a domestic hot water system with plastic pipe and fittings may not exactly be the equivalent of trying to perform surgery on oneself , but it’s close enough that you should call me before you decide that your plumber can handle it, or that Building Codes do not apply.


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